The present information relates to an engine control apparatus, a control method and a control system.
Generally, in a vehicle on which an engine is installed, a starter motor is necessary for starting the engine, and this starter motor is driven by means of a chargeable lead storage battery (hereinafter, the storage battery will be referred to as a battery). In addition, a number of auxiliary machines (electric loads) such as lamps, an air conditioner and electric power window systems which are driven by the battery are installed on the vehicle as electric equipment. Then, in order to recover the battery capacity that has been discharged to start the engine and drive the auxiliary machines, a generator (an alternator) is installed on the vehicle which is driven by the engine to generate electric power so as to charge the battery with electric power so generated.
On the other hand, in the vehicle on which the engine is installed, reducing a fuel consumption relative to a mileage or increasing the fuel economy (hereinafter, referred to as an economical running) constitutes a crucial problem to be solved, and to make this happen, a method is adopted in which the combustion efficiency of the engine is increased, or in order to suppress the wasteful fuel consumption resulting when the vehicle is idled or is under light load, the fuel supply to part of the combustion cylinders is stopped when the vehicle is idled or is under light load. In addition, there occurs a case where the engine is stopped completely for economical running when the vehicle is idled. Furthermore, a vehicle is described in Japanese Patent Publication No. 2000-204995A in which its engine is stopped when the vehicle is idled so as to prevent a battery from becoming flat by controlling an alternator while considering the charged condition of the battery.
Furthermore, a vehicle is described in Japanese Patent Publication NO. 10-153159A in which two batteries of the same type are installed on the vehicle as a battery for starting the engine and a battery for electric equipment and charging power generated by an alternator is properly allocated to the two batteries so as to prevent the batteries from being charged insufficiently to thereby realize the economical running. On the other hand, for an engine having a small number of cylinders, an auxiliary battery such as a lithium ion battery is installed in addition to a normal battery, so that an economical running engine stop is carried out in which the engine stops idling when the vehicle comes to rest. In addition, in an economical running system like this in which two batteries are installed on a vehicle, the applications of a main battery (a lead battery) and an auxiliary battery (a lithium ion battery) are defined as below.                Main battery: to be used as a power supply to the electric loads in such a state that the engine is in operation.        Auxiliary battery: to be used as a power supply to the electric loads in such a state that the engine is not in operation.        
Generally, the lead battery having an over 12V output voltage is used for mounting on the vehicle. Meanwhile, the lithium ion batteries having 4V, 8V, 12V, and 16V output voltages respectively are generally used. The lithium ion battery having the 12V output voltage is not suitable as auxiliary battery for mounting on the vehicle. In a case where a lithium ion battery having the 16V output voltage is used as an auxiliary battery, since the output voltage of the lithium ion battery is higher than the output voltage of a main battery, a DC/DC converter becomes necessary which is a voltage regulator for matching the output voltage of the auxiliary battery to the output voltage of the main battery. The DC/DC converter lowers the output voltage of the auxiliary battery when an electric load is driven by the power of the auxiliary battery and raises the output voltage of an alternator when the auxiliary battery is charged with power generated by the alternator.
Normally, a limiter for limiting an output current of the DC/DC converter is incorporated in the DC/DC converter. This limiter is made to be in operation both when the battery is charged while the vehicle is idled and when the battery is charged while the vehicle is driven at constant speed and is made to be released only when the battery is charged while the vehicle is decelerated in order to ensure the output current flowing to the lead buttery when the vehicle accelerate. While a maximum current that the DC/DC converter can supply when the limiter is in operation is, for example, on the order of 15 amperes (hereinafter, referred to as (A), but in the drawings, denoted as A), and a maximum current that the DC/DC converter can supply when the limiter is released is, for example, on the order of 20(A).
In the economical running system on which the two batteries that are configured as has been described above are installed, since a power supply to an electric load during economical running is effected by the lithium ion battery, in the event that the voltage of the lithium ion battery is low, the economical running is prohibited until the lithium ion battery is charged to a high voltage. The charging of the lithium ion battery is carried out by the alternator and the DC/DC converter.
In the twin-battery type economical running system that is configured as has been described above, however, when the lithium ion battery is charged, since the limiter of the DC/DC converter is released only when the battery is charged while the vehicle is decelerated, current that charges the lithium ion battery is not much, leading to a problem that it takes much time to charge the lithium ion battery. Due to this, when the vehicle comes to be idled in such a state that the voltage of the lithium ion battery is low, a long time is needed until an economical running is permitted which is enabled when the voltage of the lithium ion battery is high, leading to a problem that the number of times of permitting the economical running is reduced.